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Transcript of Tutorial 3&4
Rules used in this exercise
Spontaneous Potential log
Natural electric potential that develops as a result of ion movement between solutions of different salinities where CL- ions separate from NA+ ions and attracted by the shales measured by milli-volts (mv)
Origin of SP
SP currents are caused by electro motive forces in the formation represented in
1) Oil base-mud
At permeable formation , SP is -ve ( Rw<Rmf)
At im-permeable formation , SP is +ve (Rw>Rmf)
SSP : difference between sand base-line and shale base-line
2) Dry hole
3) Cased hole
due to the absence / presence of non conductive materials that provide electrical continuity between the fixed and moving electrode
occurs due to movement of NA+CL- from higher salinity to a lower one
occurs due to the flow of mu filtrate through the mud cake
SSP= -K log (Rmf eq/Rw eq)
K = 61+0.133 (T)
Rmf2 = Rmf1 X (T1+6.77 / T2+6.77)
V sh = 1 - ( sp/ssp )
T --> B.H.T
Rmf2 --> B.H
Rmf1 --> Surface Temp.
10-35 shaly sand
Fill in the blanks in the following table :
For a drilled well and shown in the next figure:
Determine formation water resistivity, Rw and Lithofacies properties of the logged section.
Is there producing zone(s)?
Rmf= 0.64 @78 F
BHT= 190 F @10,500 ft
Mean Surface Temp.= 80 F
1) Convert Rmf from Surface to BHT
2) Get Rmf eq chart
3) Get K
4) Get Rw eq from SSP rule
5) Get Rw from chart
6) Calculate V sh
Determine formation water resistivity, Rw from the SP for the two zones at 8990 and 9200 shown in the next figure.
If the Rw's differ, explain the reason why ?
Rmf= 0.64@ 90 F
BHT = 219 F
The water resistivity at 9200 decreases as the temperature increases therefore more salt can be dissolved in the water which indicates the increase in conductivity and reduction in resistivity
Tutorial 3 & 4
It's a continuous recording of the natural radiations emitted from the formation measured in (API) , most of those radiations are present in the radio active materials ( thorium - potassium - uranium ) found in clay and shales while sandstones and limestones contain very low radio active isotopes.
GR works through cased & dry holes , though the steel pipe absorb some of the gamma ray which decreases its intensity but enough GR reach the tool at the end.
Rules used in this exercise
GR - GR max
GR min - GR max
Vsh= 0.083(2 - 1)
3.7 x IGR
POST TERTIARY , CLASTIC ROCKS , LATE QUATERNARY
Vsh= 0.33(2 -1)
2 x IGR
PRE-TERTIARY , CRETACEOUS , CARBONATE
Determine the Vsh for the selected zones in the CARBONATE sequence shown in example well B , figure H-2-3
In figure H-2-4 calculate Vsh fro total counts (GR) .Assuming formations are cretaceous except formations A & B are late quaternary
Given that :
minimum CTS 12
maximum CTS 120
Draw a GR&SP for a sequence of thick formations which are from the top to bottom , SHALE , PERMEABLE LAYER, SHALE, IMPERMEABLE LAYER, SHALE, PERMEABLE LIMESTONE & RADIO ACTIVE SAND.
Figure H-2-6 is a composite log of GR and NGS zone. Determine if Zone A is radio active and explain .
Natural GR spectometer
Wael EL Basel